Onan 3.0 AJ runs, but not for long

[minibagel84]

ok, here I go. have an onan 3.0 AJ series. Took it out, cleaned it up, replaced brushes, cleaned comutator, slip rings. Replaced control relays, any damaged wire connectors.
Issue one corrected; it starts like a dream.
Issue two; would run for 10-15 minutes, under a load, then quits suddenly; not resolved.
I have rebuilt/ adjusted the carb/governor, checked the fuel flow/filter. Check spark at plug after shut down, plenty there.
Voltage under no load; 119.
Voltage under a/c load; starts at 109, slowly drops to 102 then dies.
A/C pulling 13.85 amps, 1569 watts on high cool. 
As in the similar post on the 4.0, how else can I check the coil besides letting it bite me and will a Volkswagen coil do the trick?
Note; I will check the points momentarily and get back with you.

[Rickf1985]

Can't help, I have a 2.5 AJ and can't even get it running. wrap the rope, pull the rope, repeat. Over and over. Someday I might get it to start or it may end up in the classifieds.

[pvoth1111]

starting fluid?

[DaveVA78Chieftain]

Based on this manual the AJ is a magneto based engine:
http://michaelstractors.com/forum/upload/B112/Onan%20Master%20Service%20Manual.pdf

So no, a Volkswagen coil will not work.

Dave